DESCRIPTION

The termios functions describe a general terminal interface that is
provided to control asynchronous communications ports.
Thetermiosstructure
Many of the functions described here have a termios_p argument that is
a pointer to a termios structure. This structure contains at least the
following members:
tcflag_t c_iflag; /* input modes */
tcflag_t c_oflag; /* output modes */
tcflag_t c_cflag; /* control modes */
tcflag_t c_lflag; /* local modes */
cc_t c_cc[NCCS]; /* control chars */
The values that may be assigned to these fields are described below.
In the case of the first four bit-mask fields, the definitions of some
of the associated flags that may be set are only exposed if a specific
feature test macro (see feature_test_macros(7)) is defined, as noted in
brackets ("[]").
In the descriptions below, "not in POSIX" means that the value is not
specified in POSIX.1-2001, and "XSI" means that the value is specified
in POSIX.1-2001 as part of the XSI extension.
c_iflag flag constants:
IGNBRK Ignore BREAK condition on input.
BRKINT If IGNBRK is set, a BREAK is ignored. If it is not set but
BRKINT is set, then a BREAK causes the input and output queues
to be flushed, and if the terminal is the controlling terminal
of a foreground process group, it will cause a SIGINT to be sent
to this foreground process group. When neither IGNBRK nor
BRKINT are set, a BREAK reads as a null byte ('\0'), except when
PARMRK is set, in which case it reads as the sequence \377 \0
\0.
IGNPAR Ignore framing errors and parity errors.
PARMRK If IGNPAR is not set, prefix a character with a parity error or
framing error with \377 \0. If neither IGNPAR nor PARMRK is
set, read a character with a parity error or framing error as
\0.
INPCK Enable input parity checking.
ISTRIP Strip off eighth bit.
INLCR Translate NL to CR on input.
IGNCR Ignore carriage return on input.
ICRNL Translate carriage return to newline on input (unless IGNCR is
set).
IUCLC (not in POSIX) Map uppercase characters to lowercase on input.
IXON Enable XON/XOFF flow control on output.
IXANY (XSI) Typing any character will restart stopped output. (The
default is to allow just the START character to restart output.)
IXOFF Enable XON/XOFF flow control on input.
IMAXBEL
(not in POSIX) Ring bell when input queue is full. Linux does
not implement this bit, and acts as if it is always set.
IUTF8 (since Linux 2.6.4)
(not in POSIX) Input is UTF8; this allows character-erase to be
correctly performed in cooked mode.
c_oflag flag constants defined in POSIX.1:
OPOST Enable implementation-defined output processing.
The remaining c_oflag flag constants are defined in POSIX.1-2001,
unless marked otherwise.
OLCUC (not in POSIX) Map lowercase characters to uppercase on output.
ONLCR (XSI) Map NL to CR-NL on output.
OCRNL Map CR to NL on output.
ONOCR Don’t output CR at column 0.
ONLRET Don’t output CR.
OFILL Send fill characters for a delay, rather than using a timed
delay.
OFDEL (not in POSIX) Fill character is ASCII DEL (0177). If unset,
fill character is ASCII NUL ('\0'). (Not implemented on Linux.)
NLDLY Newline delay mask. Values are NL0 and NL1. [requires
_BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
CRDLY Carriage return delay mask. Values are CR0, CR1, CR2, or CR3.
[requires _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
TABDLY Horizontal tab delay mask. Values are TAB0, TAB1, TAB2, TAB3
(or XTABS). A value of TAB3, that is, XTABS, expands tabs to
spaces (with tab stops every eight columns). [requires
_BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
BSDLY Backspace delay mask. Values are BS0 or BS1. (Has never been
implemented.) [requires _BSD_SOURCE or _SVID_SOURCE or
_XOPEN_SOURCE]
VTDLY Vertical tab delay mask. Values are VT0 or VT1.
FFDLY Form feed delay mask. Values are FF0 or FF1. [requires
_BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
c_cflag flag constants:
CBAUD (not in POSIX) Baud speed mask (4+1 bits). [requires
_BSD_SOURCE or _SVID_SOURCE]
CBAUDEX
(not in POSIX) Extra baud speed mask (1 bit), included in CBAUD.
[requires _BSD_SOURCE or _SVID_SOURCE]
(POSIX says that the baud speed is stored in the termios
structure without specifying where precisely, and provides
cfgetispeed() and cfsetispeed() for getting at it. Some systems
use bits selected by CBAUD in c_cflag, other systems use
separate fields, for example, sg_ispeed and sg_ospeed.)
CSIZE Character size mask. Values are CS5, CS6, CS7, or CS8.
CSTOPB Set two stop bits, rather than one.
CREAD Enable receiver.
PARENB Enable parity generation on output and parity checking for
input.
PARODD If set, then parity for input and output is odd; otherwise even
parity is used.
HUPCL Lower modem control lines after last process closes the device
(hang up).
CLOCAL Ignore modem control lines.
LOBLK (not in POSIX) Block output from a noncurrent shell layer. For
use by shl (shell layers). (Not implemented on Linux.)
CIBAUD (not in POSIX) Mask for input speeds. The values for the CIBAUD
bits are the same as the values for the CBAUD bits, shifted left
IBSHIFT bits. [requires _BSD_SOURCE or _SVID_SOURCE] (Not
implemented on Linux.)
CMSPAR (not in POSIX) Use "stick" (mark/space) parity (supported on
certain serial devices): if PARODD is set, the parity bit is
always 1; if PARODD is not set, then the parity bit is always
0). [requires _BSD_SOURCE or _SVID_SOURCE]
CRTSCTS
(not in POSIX) Enable RTS/CTS (hardware) flow control.
[requires _BSD_SOURCE or _SVID_SOURCE]
c_lflag flag constants:
ISIG When any of the characters INTR, QUIT, SUSP, or DSUSP are
received, generate the corresponding signal.
ICANON Enable canonical mode (described below).
XCASE (not in POSIX; not supported under Linux) If ICANON is also set,
terminal is uppercase only. Input is converted to lowercase,
except for characters preceded by \. On output, uppercase
characters are preceded by \ and lowercase characters are
converted to uppercase. [requires _BSD_SOURCE or _SVID_SOURCE
or _XOPEN_SOURCE]
ECHO Echo input characters.
ECHOE If ICANON is also set, the ERASE character erases the preceding
input character, and WERASE erases the preceding word.
ECHOK If ICANON is also set, the KILL character erases the current
line.
ECHONL If ICANON is also set, echo the NL character even if ECHO is not
set.
ECHOCTL
(not in POSIX) If ECHO is also set, ASCII control signals other
than TAB, NL, START, and STOP are echoed as ^X, where X is the
character with ASCII code 0x40 greater than the control signal.
For example, character 0x08 (BS) is echoed as ^H. [requires
_BSD_SOURCE or _SVID_SOURCE]
ECHOPRT
(not in POSIX) If ICANON and IECHO are also set, characters are
printed as they are being erased. [requires _BSD_SOURCE or
_SVID_SOURCE]
ECHOKE (not in POSIX) If ICANON is also set, KILL is echoed by erasing
each character on the line, as specified by ECHOE and ECHOPRT.
[requires _BSD_SOURCE or _SVID_SOURCE]
DEFECHO
(not in POSIX) Echo only when a process is reading. (Not
implemented on Linux.)
FLUSHO (not in POSIX; not supported under Linux) Output is being
flushed. This flag is toggled by typing the DISCARD character.
[requires _BSD_SOURCE or _SVID_SOURCE]
NOFLSH Disable flushing the input and output queues when generating the
SIGINT, SIGQUIT, and SIGSUSP signals.
TOSTOP Send the SIGTTOU signal to the process group of a background
process which tries to write to its controlling terminal.
PENDIN (not in POSIX; not supported under Linux) All characters in the
input queue are reprinted when the next character is read.
(bash(1) handles typeahead this way.) [requires _BSD_SOURCE or
_SVID_SOURCE]
IEXTEN Enable implementation-defined input processing. This flag, as
well as ICANON must be enabled for the special characters EOL2,
LNEXT, REPRINT, WERASE to be interpreted, and for the IUCLC flag
to be effective.
The c_cc array defines the special control characters. The symbolic
indices (initial values) and meaning are:
VINTR (003, ETX, Ctrl-C, or also 0177, DEL, rubout) Interrupt
character. Send a SIGINT signal. Recognized when ISIG is set,
and then not passed as input.
VQUIT (034, FS, Ctrl-\) Quit character. Send SIGQUIT signal.
Recognized when ISIG is set, and then not passed as input.
VERASE (0177, DEL, rubout, or 010, BS, Ctrl-H, or also #) Erase
character. This erases the previous not-yet-erased character,
but does not erase past EOF or beginning-of-line. Recognized
when ICANON is set, and then not passed as input.
VKILL (025, NAK, Ctrl-U, or Ctrl-X, or also @) Kill character. This
erases the input since the last EOF or beginning-of-line.
Recognized when ICANON is set, and then not passed as input.
VEOF (004, EOT, Ctrl-D) End-of-file character. More precisely: this
character causes the pending tty buffer to be sent to the
waiting user program without waiting for end-of-line. If it is
the first character of the line, the read(2) in the user program
returns 0, which signifies end-of-file. Recognized when ICANON
is set, and then not passed as input.
VMIN Minimum number of characters for noncanonical read.
VEOL (0, NUL) Additional end-of-line character. Recognized when
ICANON is set.
VTIME Timeout in deciseconds for noncanonical read.
VEOL2 (not in POSIX; 0, NUL) Yet another end-of-line character.
Recognized when ICANON is set.
VSWTCH (not in POSIX; not supported under Linux; 0, NUL) Switch
character. (Used by shl only.)
VSTART (021, DC1, Ctrl-Q) Start character. Restarts output stopped by
the Stop character. Recognized when IXON is set, and then not
passed as input.
VSTOP (023, DC3, Ctrl-S) Stop character. Stop output until Start
character typed. Recognized when IXON is set, and then not
passed as input.
VSUSP (032, SUB, Ctrl-Z) Suspend character. Send SIGTSTP signal.
Recognized when ISIG is set, and then not passed as input.
VDSUSP (not in POSIX; not supported under Linux; 031, EM, Ctrl-Y)
Delayed suspend character: send SIGTSTP signal when the
character is read by the user program. Recognized when IEXTEN
and ISIG are set, and the system supports job control, and then
not passed as input.
VLNEXT (not in POSIX; 026, SYN, Ctrl-V) Literal next. Quotes the next
input character, depriving it of a possible special meaning.
Recognized when IEXTEN is set, and then not passed as input.
VWERASE
(not in POSIX; 027, ETB, Ctrl-W) Word erase. Recognized when
ICANON and IEXTEN are set, and then not passed as input.
VREPRINT
(not in POSIX; 022, DC2, Ctrl-R) Reprint unread characters.
Recognized when ICANON and IEXTEN are set, and then not passed
as input.
VDISCARD
(not in POSIX; not supported under Linux; 017, SI, Ctrl-O)
Toggle: start/stop discarding pending output. Recognized when
IEXTEN is set, and then not passed as input.
VSTATUS
(not in POSIX; not supported under Linux; status request: 024,
DC4, Ctrl-T).
These symbolic subscript values are all different, except that VTIME,
VMIN may have the same value as VEOL, VEOF, respectively. In
noncanonical mode the special character meaning is replaced by the
timeout meaning. For an explanation of VMIN and VTIME, see the
description of noncanonical mode below.
Retrievingandchangingterminalsettingstcgetattr() gets the parameters associated with the object referred by
fd and stores them in the termios structure referenced by termios_p.
This function may be invoked from a background process; however, the
terminal attributes may be subsequently changed by a foreground
process.
tcsetattr() sets the parameters associated with the terminal (unless
support is required from the underlying hardware that is not available)
from the termios structure referred to by termios_p. optional_actions
specifies when the changes take effect:
TCSANOW
the change occurs immediately.
TCSADRAIN
the change occurs after all output written to fd has been
transmitted. This function should be used when changing
parameters that affect output.
TCSAFLUSH
the change occurs after all output written to the object
referred by fd has been transmitted, and all input that has been
received but not read will be discarded before the change is
made.
Canonicalandnoncanonicalmode
The setting of the ICANON canon flag in c_lflag determines whether the
terminal is operating in canonical mode (ICANON set) or noncanonical
mode (ICANON unset). By default, ICANON set.
In canonical mode:
* Input is made available line by line. An input line is available
when one of the line delimiters is typed (NL, EOL, EOL2; or EOF at
the start of line). Except in the case of EOF, the line delimiter is
included in the buffer returned by read(2).
* Line editing is enabled (ERASE, KILL; and if the IEXTEN flag is set:
WERASE, REPRINT, LNEXT). A read(2) returns at most one line of
input; if the read(2) requested fewer bytes than are available in the
current line of input, then only as many bytes as requested are read,
and the remaining characters will be available for a future read(2).
In noncanonical mode input is available immediately (without the user
having to type a line-delimiter character), and line editing is
disabled. The settings of MIN (c_cc[VMIN]) and TIME (c_cc[VTIME])
determine the circumstances in which a read(2) completes; there are
four distinct cases:
* MIN == 0; TIME == 0: If data is available, read(2) returns
immediately, with the lesser of the number of bytes available, or the
number of bytes requested. If no data is available, read(2) returns
0.
* MIN > 0; TIME == 0: read(2) blocks until the lesser of MIN bytes or
the number of bytes requested are available, and returns the lesser
of these two values.
* MIN == 0; TIME > 0: TIME specifies the limit for a timer in tenths of
a second. The timer is started when read(2) is called. read(2)
returns either when at least one byte of data is available, or when
the timer expires. If the timer expires without any input becoming
available, read(2) returns 0.
* MIN > 0; TIME > 0: TIME specifies the limit for a timer in tenths of
a second. Once an initial byte of input becomes available, the timer
is restarted after each further byte is received. read(2) returns
either when the lesser of the number of bytes requested or MIN byte
have been read, or when the inter-byte timeout expires. Because the
timer is only started after the initial byte becomes available, at
least one byte will be read.
Rawmodecfmakeraw() sets the terminal to something like the "raw" mode of the
old Version 7 terminal driver: input is available character by
character, echoing is disabled, and all special processing of terminal
input and output characters is disabled. The terminal attributes are
set as follows:
termios_p->c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP
| INLCR | IGNCR | ICRNL | IXON);
termios_p->c_oflag &= ~OPOST;
termios_p->c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
termios_p->c_cflag &= ~(CSIZE | PARENB);
termios_p->c_cflag |= CS8;
Linecontroltcsendbreak() transmits a continuous stream of zero-valued bits for a
specific duration, if the terminal is using asynchronous serial data
transmission. If duration is zero, it transmits zero-valued bits for
at least 0.25 seconds, and not more that 0.5 seconds. If duration is
not zero, it sends zero-valued bits for some implementation-defined
length of time.
If the terminal is not using asynchronous serial data transmission,
tcsendbreak() returns without taking any action.
tcdrain() waits until all output written to the object referred to by
fd has been transmitted.
tcflush() discards data written to the object referred to by fd but not
transmitted, or data received but not read, depending on the value of
queue_selector:
TCIFLUSH
flushes data received but not read.
TCOFLUSH
flushes data written but not transmitted.
TCIOFLUSH
flushes both data received but not read, and data written but
not transmitted.
tcflow() suspends transmission or reception of data on the object
referred to by fd, depending on the value of action:
TCOOFF suspends output.
TCOON restarts suspended output.
TCIOFF transmits a STOP character, which stops the terminal device from
transmitting data to the system.
TCION transmits a START character, which starts the terminal device
transmitting data to the system.
The default on open of a terminal file is that neither its input nor
its output is suspended.
Linespeed
The baud rate functions are provided for getting and setting the values
of the input and output baud rates in the termios structure. The new
values do not take effect until tcsetattr() is successfully called.
Setting the speed to B0 instructs the modem to "hang up". The actual
bit rate corresponding to B38400 may be altered with setserial(8).
The input and output baud rates are stored in the termios structure.
cfgetospeed() returns the output baud rate stored in the termios
structure pointed to by termios_p.
cfsetospeed() sets the output baud rate stored in the termios structure
pointed to by termios_p to speed, which must be one of these constants:
B0B50B75B110B134B150B200B300B600B1200B1800B2400B4800B9600B19200B38400B57600B115200B230400
The zero baud rate, B0, is used to terminate the connection. If B0 is
specified, the modem control lines shall no longer be asserted.
Normally, this will disconnect the line. CBAUDEX is a mask for the
speeds beyond those defined in POSIX.1 (57600 and above). Thus, B57600
& CBAUDEX is nonzero.
cfgetispeed() returns the input baud rate stored in the termios
structure.
cfsetispeed() sets the input baud rate stored in the termios structure
to speed, which must be specified as one of the Bnnn constants listed
above for cfsetospeed(). If the input baud rate is set to zero, the
input baud rate will be equal to the output baud rate.
cfsetspeed() is a 4.4BSD extension. It takes the same arguments as
cfsetispeed(), and sets both input and output speed.

RETURNVALUE

cfgetispeed() returns the input baud rate stored in the termios
structure.
cfgetospeed() returns the output baud rate stored in the termios
structure.
All other functions return:
0 on success.
-1 on failure and set errno to indicate the error.
Note that tcsetattr() returns success if any of the requested changes
could be successfully carried out. Therefore, when making multiple
changes it may be necessary to follow this call with a further call to
tcgetattr() to check that all changes have been performed successfully.

CONFORMINGTO

tcgetattr(), tcsetattr(), tcsendbreak(), tcdrain(), tcflush(),
tcflow(), cfgetispeed(), cfgetospeed(), cfsetispeed(), and
cfsetospeed() are specified in POSIX.1-2001.
cfmakeraw() and cfsetspeed() are nonstandard, but available on the
BSDs.

NOTES

Unix V7 and several later systems have a list of baud rates where after
the fourteen values B0, ..., B9600 one finds the two constants EXTA,
EXTB ("External A" and "External B"). Many systems extend the list
with much higher baud rates.
The effect of a nonzero duration with tcsendbreak() varies. SunOS
specifies a break of duration*N seconds, where N is at least 0.25,
and not more than 0.5. Linux, AIX, DU, Tru64 send a break of duration
milliseconds. FreeBSD and NetBSD and HP-UX and MacOS ignore the value
of duration. Under Solaris and Unixware, tcsendbreak() with nonzero
duration behaves like tcdrain().